Manufacture of metal hydroxids



A UNITED STATES PATENT omen.

m rooms, 0! HEIDELBEBG, GERMANY, ASSIGNOB, BY nan Maxims, TO THE CHEMICAL FOUNDATION, INC., A CORPORATION OI DELAWARE.

nanunc'r'unn or mini. nrnaonns.

ipeclflcatlon of Letters Intent.

Io Drawing. Application fled August 28, 1915, Serial Io. 47,487. Renewed June II, 1019. lerhl Io.

To all whom it may concern:

Be it known that I, Dr. Max BUCHNER a subject of the Emperor of Germany, an a resident of Heidelberg, Germany, have invented certain new and useful Improvements in the Manufacture of Metal Hydroxide; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to the manufacture of metal-hgldroxids, and more particularly to the hy oxid of aluminum in such a physical state as to be readily filterable and readily washable. The invention is particularly applicable to aluminum salts, since it permits the production of aluminum hydroxid in a readily workable and very valuable form, free from basic combinations. Furthermore, the precipitates are low in water content, only small quantities of washing water are required to be used, and are free from soluble metal combinations.

The new process comprises the utilization of metal salts capable of forming hydrates either in solution or in a solid state, which are treated with concentrated ammonia in excess, and the resulting reaction liquor containing the ammonia salts formed by the reaction, is readily drawn oil from the hydroxid precipitate. This liquor is then enriched with ammonia, to be again used as a reagent or precipitating means.

This repeated use is continued until the reagent or precipitating liquid has been sufficiently saturated or enriched to permit the crystallizing out of the ammonia salts.

The repeatedly used liquor formed during the process requlres but very slight evaporation to separate the ammonia salts in solid form.

As a precipitant I use concentrated aqueous or liquid ammonia in such quantity that there is an excess of NH, present, and it is advantageous to operate with several or successive volumes of ammonia. The enriching or regeneration of the liquor, after the reaction between the concentrated excess of ammonia and the metal salts, and after it has been drawn off the hydroxid precipitate, is accomplished by adding highly concentrated aqua ammonia, liquid ammonia, or by the introduction of ammonia gas. In the latter case, pure ammonia may be used, or residual gases containing ammonia.

Instead of enrichin the resulting liquor freed from metal hy roxid precipitate beboreits re-use, this liquor may be directly applied to a fresh quantity of metal salts and then enriched by introducing into the mixture ammonia gas from any source, that is, pure ammoma, or waste gases containing ammonia.

The metal salt solution is advantageously a saturated one.

Solid metal salts may be used either in a pulverulent. form, lumps or other form, with or without water of crystallization therein. Under some circumstances the'salt may be freed from its water of c stallization by heating, or it ma be mel in its water of crystallization. hen the melted salt is immedlately brought into contact with highly concentrated ammonia in excess, or with enriched residual liquor. Of special value is the use of .metal salts in lumps which are converted with certainty into readily washable, thick precipitates, free from basic combinations and poor in water.

In addition to ammonium, its organic derivatives may be used as precipitants, for example, anilin, ammonia combinations of the weak acids, such as ammonium carbonate, and ammonium sulfid. As heretofore stated, gaseous ammonia may be used in the form of waste gases containing ammonia, such as Mond as, coke-oven gas, etc. Instead of owing the liquid ammonia mto the metal salt solution or over the solid metal salt, the reverse may be done. The metal salt may thus be introduced into an excess of saturated aqueous ammonia, or be introduced into the residual liquor after enrichment, as heretofore stated. In any case, the quantity of ammonia must be in excess, and advantageously many times the volume theoretically required. The use of an excess of ammonia, several times the quantit required for the reaction, produces a deci edly different product from a case where the ammonia is present in amounts only suflicient to maintain the solution of alkaline. The product is more readily and immediately filterable, and not gelatinous.

The introduction into the saturated metal salt solution. of solid or molten metallic salts, is not done all at 'once, but small por- Patented Apr. 20, 1920.

sis

' operation may also be carried out with a porous partition separating the reagent liquid from the metal salt, whether the salt be in solution or in a solid form. In this manner the transformation (from ammonia combination to hydroxid) and the purification of the metal hydroxid is accomplished by osmosis. This process isa continuous one, if on the one side of the orous partition solid salt is added from time to time, and on the other side of the partition ammonia from any source is continuously supplied to the liquid. The metal hydroxid precipitate is then removed from time to time. The ammonium salt disengaged from the enriched liquor also can be removed from time to time.

As a specific example, a very useful pasty, readily cleaned precipitate is obtained 1f one kilo of aluminum sulfate be treated with four liters of aqua ammonia containing 150 to 160 gr. of NH to the liter. If the metal salt to be precipitated is not all supplied at once but is added in small quantities from time to time the filtrate or resulting liquor may be used again, in order to save ammonia. Even if the resulting ammonium sulfate liquor is heavily charged with the salt it is still ca able of taking up considerable quantities o ammonia, so that by introducing ammonia gas it is quickly regenerated for further operations.

Furthermore, the process as above explained may be carried out so that the filtrate or ammonium sulfate liquor containing ammonia in solution is immediately brought into contact with fresh quantities of metallic salts, and during the reaction gaseous ammonia is introduced.

The reaction between ammonia and aluminum salt may be carried out warm as well as cold, and even if it is carried out in the cold, reaction is completed ina very short time, and it is remarkable that from lumps the leaching or removal of the aluminum sulfate takes place very quickly. It is advantageous to so position the pieces of material that they will be acted upon readily by the ammoniacal liquor from all sides, and that the material to be acted upon lies sufliciently high in the bath, so that the ammoniacal liquor can readily flow ofi.

As above indicated, the chemical and physical properties of the precipitate cause a 11 11110131011 in the water content of the liquor, and if this reduction of water con-. I

tent is noted to any great degree, it is advantageous to add water from time to-time to replace the water lost in the precipitate. With the use of solid aluminum sulfate, as well as with the use of concentrated solutions, water of crystallization on the one hand, and solution water on the other'hand is introduced into the reaction mixture, in order to balance the mixture.

' Finally, the concentration of the metal salt solution, or the aluminum salt solution, must be considered. This must be high enough to precipitate the metal hydroxid, especially aluminum hydroxid, not in a gelatinous condition, but rather in pasty condition. The minimum concentration is to be tested in different salts during the process, and is to be fixed by such tests. It is to be noted that with the use of solid metal salts or aluminum salts that contain water of crystallization, as well as with such salts that have been dehydrated, a relatively fine granular, rapidly filterable precipitate is obtained.

According to the present process all the metal salts, and especially aluminum salts that can be converted into hydroxids may be used, and the process is suitable for the manufacture of aluminum hydroxids from pure or impure aluminum salts, such as are obtained by the action of acids on aluminum containing materials, especially with sulfuric acid. In this case the mentioned aluminum salts are filtered off from the insoluble silica residues, and by evaporation of the water are highly concentrated or saturated to such an extent that the aluminum salts will crystallize out. Naturally, these are mixed with iron and other salt impi irities.

hen operating by dialyses with a porous partition, the process is carried out as follows:

In a vessel containing strong or saturated aqueous ammonia, is inserted a porous ce or other readily permeable artition wall,

for example a frame containing a stretched and an excess pressure in the porous cell, that the precipitate does not hinder the passage of the solutions. It is advantageous to operate with an over pressure on the precipitant, whereby the reaction is accelerated, and naturally during the whole process with an excess of precipitant.

In orderto free the hydroxid precipitate from the residues of reaction salts, the cell is removed, and the contents placed in a suction apparatus, or in a filter press, and then washed. The residual solution after being again saturated with ammonia is reused.

In order to hasten the reaction, precipitant may be added on both sides of the porous partition, but it is preferable to introduce salt on one side of the partition wall and ammonia on the other side of the partition wall into the precipitating or reagent liquor.

With the repeated use of the liquor and the consequent continuous addition thereto of precipitating medium and salt on oppo site sides of the partition wall, the process is a completely continuous one, the salt being alternately introduced and the precipitate removed, while on the exterior ammonia is added and the separated ammonium salt removed.

I claim- 1. Process of producing metal hydroxids in readily filterable and readily washable form, which comprises reacting on a metal salt capable of forming a hydrate with concentrated ammonia several times in excess of the quantity required for the reaction, and removing the reaction li nor with the ammonium salts formed, an immediately using said liquor for reacting on a new quantity of salt while introducing ammonia gas thereinto.

2. Process of producing metal hydroxids in readily filterable and readily washable form, which comprises reacting on metal salt in lumps capable of forming a hydrate wlth concentrated ammonia several times in excess of the quantity required for the reaction, and removing the reaction liquor with the ammonium salts formed, and immediately using said liquor for reacting on a new quantity of salt while introducing ammonia gas thereinto.

3. Process of producing metal hydroxids in readily filterable and readily washable form, which comprises reacting on metal salts capable of forming hydrates with ammonia several times in excess of the quantity required for the reaction, adding salt from time to time and adding ammonia from time to time, removing the reaction liquor with the ammonium salts formed and adding ammonia sufiicient to restore the strength of the solution for reintroduction into the cycle of operations.

4. Process of producing metal hydroxids in readily filterable and readily washable form, which comprises reacting through a porous diaphra m on a metal salt capable of forming hy rate with ammonia several times in excess of the quantity required for the reaction, adding salt from time to time, and adding ammoma from time to time, re-

moving the reaction liquor with the am-v monium salts formed, and regenerating the liquor in ammonia for re-introduction into the cyple of operations.

5. rocess of producing metal hydroxide in readily filterable and readily washable form, which comprises reacting through a porous diaphragm on a metal salt ca able of forming a hydrate with a solution 0 ammonia several times in excess of the quantity required for the reaction, and maintaining a supply of salt on one side of the diaphra m and a supply of ammonia on the other side of the diaphragm.

In testimony that I claim the foregoing as my invention, I have signed my name in presence of two subscribing witnesses.

DR. MAX BUCHNER.

Witn:

Hmmr Hssm, Armor Sonnommz. 

